With the development of front loading washing machines there has been a growing need for low sudsing detergent compositions and suds depressants. To obtain sufficient control of the sudsing of such compositions, particularly in some machines used on the continent of Europe where the washing temperatures can be as high as 95.degree. C, has proved very difficult. It has proved especially difficult to find effective suds-depressants for nonionic surfactants. Thus high molecular weight fatty acids or soaps, which are effective with anionic surfactants, are almost useless with nonionics. Silicones and certain waxes (for instance as described in British Patent Applications 35877/72, 1370/74, 10734/72, 22552/74) are effective at suitable rather high levels in solid nonionic based detergent compositions, but the former tend to lose their effectiveness after a few hours storage in liquid detergents and it has so far proved impossible to keep the latter dispersed uniformly for long periods in aqueous liquid detergent compositions. All these, and, so far as we are aware, all other known suds-depressants tend to reduce the available cleaning power of the detergent compositions whether solid or liquid.
It has now been discovered that certain mono and polyalkoxy substituted surfactants having the terminal hydroxyl of the alkoxy group acylated by certain monobasic acids (referred to hereinafter as "capped" surfactants) wherein the capped surfactants have certain defined levels of components with specific HLB (hydrophilic lipophilic balance) values, are outstandingly effective suds-depressants for nonionic and zwitterionic detergents and even soaps. At the same time, the "capped" surfactants have substantially the same detergency characteristics as the non-capped precursor surfactants so that they may be used as suds-depressants in, say, nonionic detergent compositions without imposing any additional load on the performance of the composition. The "capped" surfactants may be used to render such detergent compositions substantially non-sudsing even in some washing machines prone to generate suds strongly, or they may be used to provide a low degree of sudsing, as generally preferred by the users of such products.
The novel suds-depressants have the further advantage that their suds-depressant action is greatest at high temperatures, where over-sudsing is most troublesome. In warm water, as in the hand wash, a moderate to low level of suds can be provided, and the suds which are formed are unusually stable. The suds-depressants also enhance the rinsing characteristics of the detergent composition.
Compounds of this general type having 3 to 50 alkoxy groups per molecule are described in Rohm & Haas DAS 1,243,312 as low sudsing surfactants compatible with nonionic and ionic surfactants. There is no general disclosure of a compound with less than 3 alkoxy groups per molecule, and no specific disclosure of a compound with less than 7.5 ethoxy groups per molecule, and no suggestion at all of the surprising suds depressant action of certain alkoxy derivatives in combination with other surfactants. Percentages and ratios are by weight and temperatures in degrees Centigrade unless otherwise indicated.